This invention concerns an article of black silver color applicable to exterior parts, spectacle frames, stationeries, personal ornaments and various kinds of accessories.
Heretofore, the following chemical treatment has been known as one of the methods for obtaining a high quality dark silver color. This is a chemical treatment of immersing a material previously coated with a metal such as zinc, aluminum and nickel or the metal material per se such as zinc, aluminum and nickel into a solution mainly composed of sodium chromate or sodium bichromate and thereby forming a chromium oxide layer on the surface. It has been also known to use a chemical treatment of immersing material, previously coated with a metal such as zinc, aluminum and nickel or the metal material itself such as zinc, aluminum and nickel, into a solution composed of a nickel chloride solution with hydrogen sulfide, thereby forming a nickel sulfide coating layer on the surface.
These known chemical treatments are restricted in view of the material, the layer thickness of the coating layer formed thereby is extremely thin being at most about 0.1 .mu.m, and the coating layer lacks a dense texture. Accordingly, there has been a problem such relating to corrosion resistance and abrasion resistance.